Process for biological remediation of vaporous pollutants

ABSTRACT

This invention relates to a process for remediating vaporous pollutants which comprises passing a vaporous stream containing one or more of pollutants through a bioreactor, the bioreactor comprising a plurality of biologically active bodies, the biologically active body comprising a macroporous substrate and one or more of microorganisms capable of remediating one or more of said pollutants, wherein the substrate is fabricated from a decomposition-resistant material. The present invention further provides an apparatus for this process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for remediating vaporouspollutants. More particularly, the present invention relates to aprocess for remediating vaporous pollutants using a carbon-coatedsubstrate that supports pollutant-remediating microorganisms.

2. Description of the Prior Art

There are three common ways to remove vaporous or gaseous pollutantsfrom gas- or air-streams. One common method is to pass contaminatedgases over an absorbent, such as activated carbon particles, whichabsorbs the pollutants contained in the gases. However, this type ofremoval requires a large volume of absorbents and creates the problem ofdisposal or regeneration of the spent absorbents.

The second common method is to pass contaminated gases through abiologically activated sludge that contains microorganisms which canmetabolize and remediate the pollutants. This type of bioremediationprocesses are disclosed, for example, in U.S. Pat. Nos. 4,544,381 and4,894,162. These processes also have disadvantages in that they create alarge volume of sludge that needs to be disposed of and the rate ofremediation is limited by the solubility of the pollutants in thesludge.

The other common method is to pass contaminated gases through a bed ofsubstrates in a bioreactor which carries microorganisms that degrade thepollutants contained in the gases. The prior art substrates used in thismethod have mainly been decomposable organic matters, such as peat, woodchips and other composts. For example, U.S. Pat. No. 4,662,900 disclosesa variation of this substrate method. However, the use of decomposableorganic matters as the substrates for supporting and carrying thebioremediating microorganisms may be disadvantageous in that thesubstrates decompose and settle with time. In addition, the organicsubstrates are not dimensionally stable, changing their dimension withthe age of the substrate and the humidity level in the bioreactor. Suchsettlement and dimensional instability change the flow pattern of thegases fed through the bioreactor, creating undesirable flow patterns,and often create channeling that directs the influent gases to bypasssubstantial sections of the bioreactor, diminishing the efficiency ofthe reactor. In addition, the organic substrates do not have appropriateconfigurations to allow the gases to pass through without a substantialpressure drop, and the organic substrates tend to get clogged as thebiomass density increases in the reactor. Therefore, the prior artbioreactors require a high inflow pressure feed the contaminated gases.

Therefore it would be desirable to provide a bioreactor for remediatingvaporous or gaseous pollutants that is highly efficient and does notdiminish in efficiency during its operation.

SUMMARY OF THE INVENTION

The present invention provides a process for remediating vaporouspollutants which comprises passing a vaporous stream containing one ormore of pollutants through a bioreactor, the bioreactor comprising aplurality of biologically active bodies, the biologically active bodycomprising a macroporous substrate and one or more of microorganismscapable of remediating one or more of said pollutants, wherein thesubstrate is fabricated from a decomposition-resistant material. Inaddition, the bioreactor further comprises a feeding means that suppliesa solution of nutrients and buffers.

The present invention further provides a process for remediatingvaporous pollutants which comprises passing a vaporous stream containingone or more of pollutants through a bioreactor, the bioreactorcomprising a plurality of biologically active bodies and a plurality ofopen space bodies, the biologically active body comprising a macroporoussubstrate and one or more of microorganisms capable of remediating oneor more of said pollutants, wherein said substrate is fabricated from adecomposition-resistant material.

Additionally, the present invention provides an apparatus forpurification of a gaseous stream containing one or more pollutants bybiodegradation with one or more microorganisms capable of metabolizingone or more of said pollutants, said apparatus comprising: a reactorhaving an inlet for inflow of the gaseous stream, the reactor comprisinga plurality of biologically active bodies which comprise macroporoussubstrates and one or more of microorganisms capable of remediating oneor more of the pollutants; an outlet for outflow of an effluentgas-stream in which the concentration of at least one of the pollutantsis less than the concentration of the gaseous stream at the inlet; and ameans to supply a solution of nutrients and buffers, wherein the poroussubstrates are fabricated from a decomposition-resistant material. Thereactor may further comprises a plurality of open space bodies.

BRIEF DESCRIPTION OF THE FIGURE

The invention will be more fully understood and further advantages willbecome apparent when reference is made to the following description ofthe invention and the accompanying drawings in which:

FIG. 1 is a cross-sectional side view of a vertical reactor for use in apreferred embodiment of the invention.

FIG. 2 is a graphic presentation of the benzen content of the effluentair stream for Example 3.

FIG. 3 is a graphic presentation of the toluene content of the effluentair stream for Example 3.

FIG. 4 is a graphic presentation of the ethylbenzene content of theeffluent air stream for Example 3.

FIG. 5 is a graphic presentation of the m- and p-xylene contents of theeffluent air stream for Example 3.

FIG. 6 is a graphic presentation of the o-xylene content of the effluentair stream for Example 3.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, there is provided a processfor remediating vaporous pollutants which comprises passing avaporous-stream, having one or more of pollutants, through a bioreactorwhich comprises a plurality of biologically active bodies. Thebiologically active body comprises a macroporous substrate, and one ormore of microorganisms that are capable of metabolizing at least one ofthe pollutants contained in the vaporous-stream. The bioreactor mayfurther comprise open or substantially open space bodies (open spacebodies) that are intermixed with the biologically active bodies. In thepreferred embodiments of the present invention, the porous substrate orthe porous substrate and the open space body are coated with anabsorbent that is capable of absorbing one or more of the pollutantscontained in the influent stream.

The present invention will be better understood by those skilled in theart by reference to FIG. 1, as an illustration. Referring to FIG. 1, thebioreactor 1 comprises a packed column 2, which comprises biologicallyactive bodies 3 and, optionally, open space bodies 4. The biologicallyactive bodies and the open space bodies are placed on top of a ventedsupport layer 5, which may be a perforated plate fabricated from a metalor plastic. The bioreactor further comprises an inlet 6 and an outlet 7for the gases. The inlet of the gases may be placed at the lower end ofthe bioreactor, as shown in FIG. 1, or at the top of the reactor, andthe outlet of the gases should be placed at the other end of thebioreactor opposite to the inlet. During operation of the bioreactor,nutrients and water need to be provided. Nutrients, such as carbon andenergy sources and minerals, may be added through use of known additivessuch as fish meal peptine, soybean flour, peanut oil, cotton seed oil,and usually salts capable of providing phosphate, sodium, potassium,ammonium, calcium, sulfate, chloride, bromide, nitrate, carbonate orlike ions. Consequently, the bioreactor additionally comprises an inlet8 and outlet 9 for an aqueous solution containing nutrients and buffers(feed mixture). The feed mixture is fed into the bioreactor at the topthrough sprayers 10, and allowed to flow down the column and accumulatedat the bottom of the reactor. Alternatively, the feed mixture may be fedat different locations of the reactor by providing any inletconfigurations that effectively and evenly distribute the feed mixtureto the biologically active bodies. The accumulated feed mixture iswithdrawn through a conduit or an outlet 9 to an external reservoir iiin which the pH and the nutrient concentration of the collected feedmixture are analyzed. Based on the analyses of the mixture, a pHcontrolling agent, such as a solution of an acid or a base, andnutrients are added to the external reservoir. The re-conditioned feedmixture is then recycled to the top of the bioreactor. The feed mixturemay be supplied to the bioreactor continuously or intermittently. Thepresent bioreactor may also have additional water feeding mechanismsthroughout the bioreactor using any effective feeding means known in theart.

If the present bioreactor is configured to feed the gas-streams into thebottom of the reactor, optionally, the inlet of the gas-stream may beplaced below the level of the accumulated feed mixture, thereby theinfluent gases are saturated with water and a portion of water solublepollutants contained in the influent gases are stripped before the gasescome in contact with the biologically active bodies.

The present bioreactor can be adapted to remediate pollutants under bothaerobic and anaerobic conditions. If aerobic microorganisms are employedto remediate pollutants, sufficient oxygen must be presented in thegases entering the reactor to prevent deprivation of oxygen. Oxygen canbe conveniently supplemented in the form of pure oxygen or air throughthe influent gas-stream 6 or at any stage of the reactor column byproviding additional inlets. For aerobic reaction conditions,preferably, the oxygen concentration of the fluid or moisture condensateexisting around the microorganisms should be higher than 1 ppm (partsper million). If an anaerobic remediation is desired, the influent gasesshould not contain appreciable amount of oxygen or any known oxygenscavenger known in the art can be added to the gases and/or to the feedmixture.

The substrate of the present invention is formed from any organic orinorganic material that is decomposition-resistant and is capable offorming a solid body. The term decomposition-resistant as used hereinindicates that the material does not substantially biodegrade within thenormal service life of the substrate, which is at least about 5 years.Illustration of useful materials for fabrication of the substrate arethermoplastics such as polyamides, e.g., nylon 6, nylon 6/6, nylon 4/6,nylon 10, nylon 12 and the like; polyesters, e.g., poly(ethyleneterephthalate), poly(butylene terephthalate), polycarbonate, and thelike; polyacrylics, e.g. polyacrylic acid, poly(methylacrylic acid),poly(methyl acrylate), poly(methyl methacrylate), poly(ethylmethacrylate), polyacrylonitrile, polycarylamide, poly(methacrylamide)and the like; polyolefins, polyethylene, polypropylene, polybutylene andthe like; elastomeric polymers, e.g., ethylene-propylene rubber,styrenic block copolymers, nitrile rubber and the like; polystyrene;polyvinyl chloride; polyvinyls, e.g., polyvinyl alcohol, poly(vinylmethyl ether), poly(vinyl methyl ketone), poly(vinyl pyrrolidone) andthe like; as well as blends and copolymers thereof. Other usefulpolymeric materials for use in the fabrication of the polymericsubstrate are polyurethanes such as those derived from reaction ofdiisocyanates such as toluene diisocyanates, diphenyl methanediisocyanates, hexamethylene 1,6-diisocyanate, dicyclohexylmethanediisocyanate, 1,5-naphthalene diisocyanate, p-phenylene diisocyanate,m-phenylene diisocyanate, 2,4-toluene diisocyanate, 4,4'-diphenylmethanediisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate,3,3'-dimethyl-4,4'-biphenyl diisocyanate, 4,4'-diphenylisopropylidienediisocyanate, 3,3'-dimethyl-4,4'-diphenyl diisocyanate,3,3'-dimethyl-4,4'-diphenylmethane diisocyanate,3,3'-dimethoxy-4,4'-biphenyl diisocyanate, dianisidine diisocyanate,toluidine diisocyanate, hexamethylene diisocyanate,4,4'-diisocyananodiphenylmethane and the like, and diols such asglycerin, trimethylopropane, 1,2,6-hexane triol, methyl glycosidepentaerythritol, sorbital sucrose, ethylene glycol, diethylene glycol,hydroxy terminated polyesters formed by direct esterification ofdicarboxylic acid with an excess of a difunctional alcohol such aspoly(tetramethylene adipate) , poly (ethylene adipate) , poly(1,4-butylene adipate) , poly(1,5-pentylene adipate) , poly(1,3-butyleneadipate) , poly (ethylene succinate) , poly (2,3-butylene succinate),polyether diols such as those prepared by reaction of a compound havingactive hydrogens such as di alcohols, poly alcohols, di phenols,polyphenols, aliphatic diamines or polyamines and aromatic diamines orpolyamines with alkylene oxides such as styrene oxide, butylene oxide,propylene oxide, epichlorohydrin or mixtures of these alkylene oxides,ethylene diamine, diethylene triamine and 4,4-phenyl-methane diamine.

In the preferred embodiments of this invention, the substrate is formedfrom open-celled polyurethanes, such as cross-linked polymeric materialswhich can be foamed with an appropriate foaming agent such as nitrogen,helium, carbon-dioxide, azodicarbonamide and the like, to form opencelled foams.

In the particularly preferred embodiments of the invention, thesubstrate is formed from cross-linked polyurethanes. Such materials canbe obtained from commercial sources or prepared in accordance with knowntechniques. For example, such materials may be obtained by reactingisocyanate prepolymers with water (in which diamines or polyamines areoptionally contained as chain lengthening agents), or as cross-linkingagents or by reacting a suitable polyol with a suitable diisocyanate orpolycyanate reagent. Suitable polyols include long chain aliphatic diolsand polyoxyalkylene ethers. The isocyanate prepolymers have isocyanateend-groups and are prepared by reacting poly oxyalkylene ethers with anexcess of diisocyanate or polyisocyanates. Illustrative of usefulpolyoxyalkylene ethers are those which have a molecular weight of fromabout 500 to about 10,000, preferably from about 2,000 to about 8,000,which have at least two active hydrogens and which contain at least 30%by weight based on the total weight of the polyethers of oxyethylenegroups. Other useful oxyalkylene groups include oxypropylene,oxybutylene and the like. Polyethers of this type are produced byreacting compounds which have reactive hydrogen atoms such asdialcohols, polyalcohols, diphenols, polyphenols, aliphatic diamines,aliphatic polyamines, aromatic diamines, or aromatic polyamines with asuitable alkylene oxide such as ethylene oxide, propylene oxide,butylene oxide, styrene oxide and the like. Suitable diisocyanatesinclude toluene 4,4'-diisocyanate, toluene 2,4-diisocyanate, toluene2,2-diisocyanate, diphenylmethane 4,4'-diisocyanate, diphenylmethane2,4'-diisocyanate, diphenylmethane 2,2'-diisocyanate, toluene2,6-diisocyanate, hexamethylene 1,6-diisocyanate and useful diamines andpolyamines include aliphatic, cycloaliphatic and aromatic di- andpolyamines such as ethylene diamine, hexamethylene diamine, diethylenetriamine, hydrazine, guanidine, carbonate,N,N,'-diisopropylhexamethylene diamine, 1,3-bisaminomethylbenzene,N,N'-bis-(2-aminopropyl)- ethylene diamine, N,N,'-(2-aminoethyl)ethylene diamine, 4,4'-diaminodiphenyl methane,4,4'-dimethylamino-3,3'-dimethyldiphenyl methane,2,4'-diamino-diphenylmethane, 2,4-diaminotoluene, 2,6-diaminotoluene andthe like.

The substrate of the present invention may be fabricated into differentshapes, including spheres, cubes, rectangles, cylinders, irregularshaped objects and the like; to accommodate different needs of differentbioreactor configurations and applications. The size of the substratemay vary widely in longitudinal dimension of length and traversedimensions of thickness, width and diameter. Preferred sizes of thesubstrate range from about 0.3 cm to about 30 cm. More preferred sizesare from about 1 cm to about 15 cm, and most preferred sizes are fromabout 2 cm to about 8 cm.

In the preferred embodiments of the present invention, the substrate isa porous substrate that has interconnected throughpores, and preferably,the throughpores are macropores. The term macropore as used hereinindicates an average pore diameter of equal to or larger than about 0.1cm, preferably equal to or larger than about 0.15 cm, and morepreferably equal to or larger than about 0.2 cm. The throughpores withinthe substrate not only increase the surface area of the substrate wheremicroorganisms can attach and grow, thereby increasing the biomassdensity within the bioreactor, but also provide additional pathways forthe influent gases to travel, thereby reducing the pressure drop betweenthe inlet and outlet of the bioreactor. The macropores also providepathways for the feed mixture to travel to the microorganisms. Inaddition, the macropores of the substrate lessen the likelihood of thethroughpores from being clogged as the biomass density within thesubstrate increases.

The throughpores of the substrates preferably creates from about 40volume % to about 98 volume % of voids within the substrates, morepreferably from about 60 volume % to about 96 volume %, and mostpreferably from about 85 volume to about 95 volume %.

The bioreactor of the present invention may further comprise open spacebodies that are inter-dispersed among the biologically active bodies.The bioreactor may comprise from about 10 to 90 volume % of biologicallyactive bodies and from about 90 to about 10 volume % of open spacebodies. While it is not wished to be bound by any theory, it is believedthat inter-dispersing the biologically active bodies and the open spacebodies allows the open space bodies to act as redistributors that areinterdispersed throughout the reactor, which promote efficient deliveryof the feed mixture and oxygen to the biologically active bodies, andefficient removal of metabolic products from the biologically activebodies, especially when the biomass density in the bioreactor reaches alevel in which the biomass blocks some of the pores of the substrates.In addition, the open space bodies ensure that all or substantially allof the internal and external surfaces of the biologically active bodiesare accessible to the influent gases by interrupting the compaction ofthe biologically active bodies in accordance with their geometricalshapes.

The open space bodies are comprised basically of a rigid outer-frameworkwhich skeletally defines the open structure having a plurality ofpassages thereto. The size and shape of the open space bodies are notcritical, and can vary widely in longitudinal dimension of length andtraverse dimensions of thickness, width and diameter. However, the sizeof the outer-framework of the bodies must not be large enough to allowthe biologically active bodies to move into the open region of the openspace bodies. Preferred sizes of the open space bodies range from about0.3 cm to about 30 cm. More preferred sizes are from about 1 cm to about15 cm, and most preferred sizes are from about 2 cm to about 8 cm.

The composition of the open space bodies may vary widely. The onlyrequirement is that the material is suitable for use as a substrate in abioreactor, and is suitable for use in microbial processes. For example,the bodies may be formed from organic materials or inorganic materials.Illustrative of useful inorganic materials for fabrication of the openspace bodies are ceramics such as bentonite, kaolinite, kieselguhr,diatomaceous earth, aluminum, silica, zirconia, barium titanate,synthetic carbides, synthetic nitrides and synthetic borides, glassessuch as soda-lime-silica glasses, lead glasses, borosilicate glasses,laser glasses, silica glasses, and glass-ceramics and the like. Suitableorganic materials for fabrication of the open space bodies are polymerssuch as polyamides, polyesters, polyester carbonates, polycarbonates,polyolefins and the like. Preferably, the open space bodies are moldedof a rigid plastic such as polypropylene or polyethylene.

In the preferred embodiments of the present invention, the substrates orthe substrates and the open space bodies are coated with an absorbentfor at least one of the pollutants contained in the influent gases.Preferably, the entire internal surface, i.e., the surface of thethroughpores, and the external surface of the substrate are coated withan absorbent. Illustrative of useful absorbents are carbons such ascoal, charcoal, carbon black, activated carbon, and activated charcoal;silica gel; active clays; zeolites; hydrophobic and ion exchange resins,molecular sieves and the like. Of these, the preferred are coal,charcoal, carbon black and activated carbon. Suitable absorbents are inparticulate form and preferably is porous to provide for greater surfacearea. Although any size or shape of particulate absorbents may beutilized, preferably, suitable absorbents are of a size such that atleast 70% of the absorbent particles are smaller than 44 microns toprovide high surface area. In addition, suitable absorbents, preferably,have an average particle size of at least 25 microns since grinding theabsorbents to obtain a finer particle size significantly increases thecost of the abosorbents.

The substrates and the open space bodies are coated with the absorbentby conventional impregnation techniques, such as immersion of thesubstrate and the body in a suspension of the absorbents in water or anorganic solvent. The coating suspension further comprises a binder, asuspension aid, and a viscosity enhancer.

There is a tendency for binders to decrease the efficiency of anabsorbent by diminishing the abosorbent's capacity or by interferingwith a pollutant's access to the absorbent, e.g., binder envelops theabsorbent. Consequently, suitable binders should only minimally, if atall, interfere with the absorbing property of the absorbents. It hasbeen found that binders having a low Tg (glass transition temperature)function as more effective binders. In preferred embodiments of thisinvention, an effective binder has a Tg of less than or equal to about100° C. In more preferred embodiments, the effective binder has a Tgless than equal to about 50° C; in most preferred embodiments, equal toless than about 25° C. Examples of suitable binders include celluloseesters, cellulose ethers, polymers and copolymers of vinyl esters suchas vinyl, acetate, acrylic acid esters, and methacrylic acid esters;vinyl monomers such as such as styrene, acrylonitrile and acrylamide;dienes such as butadiene and chloroprene; natural rubber; and syntheticrubber such as styrene-butadiene. More detailed discussion of suitablebinders is disclosed in copending patent application Ser. No.07/763,735, filed Sep. 23, 1991.

The absorbent suspension of this invention contains a suspension aid toprovide a uniformly dispersed suspension. Although any suspension aid orsurfactant known in the art may be utilized, it has been found thatpreferred suspension aids are di-anionic, polyanionic, and net neutralor net negative zwitterionic dispersants, and that preferred suspensionaids derive their anionic charges from functionalities selected from thegroup consisting of sulfonate, sulfate, sulfite, phosphate, phosphite,phosphonate, carboxylate and combinations thereof. In other preferredembodiments, polyanionic polypeptides, such as sodium caseinate arepreferred. Illustrative of suitable suspension aids are ammoniumcaseinate, fatty acid salts, e.g., fatty acid sulfonates, alpha-olefinsulfonates, naphthalene sulfonates, biphenyl sulfonates, alcoholsulfonates, or phosphate counterparts to the above sulfonates. Thepresent absorbent suspension further comprises a viscosity enhancer orsettlement retardant in order to prevent rapid settlement of theabsorbent in the suspension. Illustrative of suitable viscosityenhancers are carrageenan, locust bean gum, agar, alginin, pectin, gums,e.g., guar gum, locust bean gum, xanthan gum, and cellulosic thickeners,e.g., carboxymethylcellulose and carboxy 2-hydroxyethyl cellulose. Moredetailed discussion of suitable suspension aids and viscosity enhancersis disclosed in copending patent application Ser. No. 07/878,105, filedMay 4, 1992.

The microorganisms used in the practice of this invention are anaerobicor aerobic microorganisms selected to degrade target pollutants in thegaseous or vaporous streams in ways well known in the art. Themicroorganisms can be employed as a pure strain or as a consortium ofmicroorganisms. Although anaerobic microorganisms often degradepollutants at a slower rate than aerobic microorganisms, an anaerobicprocess may be required to degrade a pollutant or an intermediateproduct of an aerobic process to an non-toxic level or to anon-pollutant material. Useful microorganisms may vary widely and may benaturally occurring microorganisms or may be genetically engineeredmicroorganisms. The only requirement is that the microorganisms arecapable of metabolizing the target pollutant(s) to the required effluentlevels over the required period of time. In the preferred embodiments ofthe invention, the microorganism are obtained from thepollutant-containing waste stream or from soil which has been in contactwith the waste stream.

The vaporous pollutants that can be remediated with the presentbioreactor may also vary widely. The only requirement is that at leastone of the materials can be degraded or metabolized by an aerobic oranaerobic microorganism. The materials may be organic or inorganic.Illustrative of such organic pollutants are phenolic materials such asphenol, the cresols, resorcinols, catechol, halogenated phenols as forexample, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol,2,4-dichlorophenol, pentachlorophenol, nitrophenols as 2-nitrophenol and4-nitrophenol and 2,4-dimethylphenol. Another important class of organicpollutants consists of aromatic hydrocarbons, such as benzene, toluene,xylenes, ethylbenzene, and so forth. Polynuclear aromatic hydrocarbonsare an important subclass as represented by naphthalene, anthracene,chrysene, acenaphthylene, acenaphthene, phenanthrene, fluorene,fluoranthene, naphthalene, and pyrene. Still other materials arehalogenated alkanes such as trichloroethane and the like.

In the preferred embodiments of this invention the materials are vaporsof those which are common in waste streams from industrial manufacturingfacilities, including petroleum distillation facilities. For example,various substituted and unsubstituted phenols such as phenol,chlorophenols and nitro-phenols, and aromatics such as benzene arepreferred pollutants for treatment in the process of this invention, andsubstituted and unsubstituted phenols, especially phenol, are the mostpreferred pollutants. Phenol is found in waste streams of phenolmanufacturers, of phenol users as phenol resin producers, of coal tarprocessing facilities, of wood pulping plants and other facilitiespracticing delignification. This is not to say that the process can ormust be practiced only with such streams. The process which is theinvention herein may be practiced on any feed containing levels of oneor more materials which are to be reduced.

The initial concentration of materials contained in the vaporous orgaseous stream used in the process of this invention may vary widely.One of the advantages of this invention relative to prior artbioremediation processes is that vaporous streams containing relativelyhigh amounts of materials to be removed or reduced in concentration canbe treated. In addition, the absorbent particles coated on the substrateof the present invention act as a buffer for intermittent inflows ofhigh concentration of pollutants that may be high enough to inactivatethe pollutant-remediating microorganisms. The absorbents quickly absorbthe incoming pollutants and release them slowly such that themicroorganisms are not rendered inactivated by the intermittent inflowof a high pollutant concentration and the microorganisms have arelatively constant supply of pollutants to metabolize. Through thisabsorption and desorption process, the absorbents on the substrates areregenerated and have a long service life.

The present vapor remediation bioreactor, unlike prior art bioreactorsemploying decomposable substrates, provides a long service life and animproved remediation-efficiency, as well as stable performancesregardless of the age of substrate and the fluctuating pollutantconcentration in the inflow. The present biologically active bodies arenot fabricated from a decomposable material and, thus, are dimensionallystable. Therefore, the pollutant-remediating bodies in the presentbioreactor do not change their configuration during operation of thereactor, and consequently, the flow pattern of the gases to beremediated in the bioreactor does not change with time, resulting inconsistent and stable remediation result.

The following examples are presented to more particularly illustrate theinvention and are not to be construed as limitations thereon.

EXAMPLES Example 1

This example is an illustration of the preparation for a suitableabsorbent-coating composition.

A 2.5% ammonium caseinate solution was prepared by adding 1 ml of 20%ammonium hydroxide into 200 ml of distilled water and then adding 5 g ofcasein, which is available from National Casein Co., Chicago, Ill.,while stirring rapidly to dissolve the casein particles completely. Into491 ml of distilled water, 100 ml of the ammonium caseinate solution wasadded and stirred at about 90 rpm for 20 minutes. To the resultingdiluted ammonium caseinate solution, 177 g of powdered activated carbon(PAC), type C, which is available from Calgon Corp, while agitating at260 rpm. The speed of agitation was decreased to about 80 rpm and theslurry was stirred for about 31/2 hour to remove gas bubbles. Theagitation speed was then increased to about 260 rpm and rapidly 233 mlof a carboxylated acrylate latex adhesive, Synthemul 40404, which isavailable from Reichold Corp was added. The mixture was continuouslystirred for an additional 30 minutes and then very slowly 2.5 g ofcarboxymethyl cellulose, high viscosity grade C5013, which is availablefrom Sigma Chemical, was added. The resulting mixture was continuouslystirred for another 1.5 hours, and then the agitation speed was reducedto about 40 rpm and stirred overnight to completely dissolve thecarboxymethyl cellulose.

Example 2

This example is an illustration of a suitable coating process.

A stiff reticulated polyether foam, SIF-2 ZS15D, which is available fromFoamex, Inc., Pa, having a nominal pore distribution of 15±5 pores perinch, was cut into cubes of 0.5×0.5×0.5 inches. The cubes were immersedin the slurry prepared in Example 1, and squeezed 4 to 5 times to removeentrapped air. The cubes were recovered from the slurry and passedthrough a pair of rollers having a 1.02 mm gap to remove excess slurry.The cubes were than air dried for 3 days. The resulting cubes hadapproximately 0.55 lbs of PAC when normalized to a cubic foot.

Example 3

This example demonstrates the superior property of the present substratecoated with an absorbent, PAC.

Wild-type microorganisms that can metabolize a mixture of benzene,toluene, ethylbenzene and xylene were isolated from a soil sample by thefollowing procedure. 0.5 g of soil from an abandoned drum yard wasplaced into 50 ml of a nutrient medium having the following composition:0.40 g/l of (NH₄)₂ SO₄, 0.14 g/l of KH₂ PO₄, 0.18 g/l of K₂ HPO₄, 0.20g/l of MgSO₄ -7H₂ O, 0.10 g/l of CaCl₂, 0.01 g/l of disodium EDTA, 0.05g/l of yeast extract and 0.1 ml of trace metals prepared in accordancewith the procedure outline in J. Gen. Microbiology, Brandis et al.,126,249-252 (1981). To the nutrient containing the soil sample, 10 μl ofBTEX (7.9 vol % benzene, 60.5 vol % toluene, 15.8 vol % ethylbenzene,14.2 vol % m-xylene and p-xylene mixture, and 1.6 vol % o-xylene) wereadded three times a day for one week. 2 ml of this culture was thentransferred to a flask containing 50 ml of the same nutrient medium andthe same proportion of BTEX. In 2 weeks thereafter, the cell density ofthe culture reached an adequate level, which was defined to be A₆₀₀ ofabout 0.74 when measured in a 1 cm path length cuvette using a VarianDMS 200 UV/VIS spectrometer. The culture was again transferred to 2liter of the nutrient medium containing the same proportion of BTEX.Within 3-5 days the cell density reached the above-defined adequatelevel.

Four glass columns having an inside diameter of 6.6 cm and a height of71 cm (volume of each being about 2.7 liter) were packed as follows.Column 1 was packed with, in 1:1 volume ratio, 0.5×0.5×0.5 inch cubes ofuncoated polyether foam and 1 inch diameter rigid spherical open spacebodies, which is available from Jaeger Products, Inc., under a tradedesignation of Tripack; column 2 was packed with, in 1:1 volume ratio,0.5×0.5×0.5 inch cubes of coated polyether foam as prepared in Example 2and 1 inch Tripack; column 3 was packed with 0.5×0.5×0.5 inch cubes ofuncoated polyether foam; and column 4 was packed with 0.5×0.5×0.5 inchcubes of coated polyether foam as prepared in Example 2.

The columns were fitted into a reactor configuration similar to thatshown in FIG. 1. The top of the column was fitted with a rubber stopperequipped with an outlet for the gas and an inlet for the nutrient. Aglass frit was place at the bottom of the column to function both as aholder for the substrates and a sprager. A side arm was inserted throughthe wall of the column as an outlet for the accumulated nutrient at alevel about 3.5 cm above the frit. The fluid exiting the side arm wascollected into a 500 ml flask and recirculated to the top of the columnafter its pH was adjusted with 2N NaOH. The flow rate of the nutrientwas about 12 ml per minute. Air containing the pollutants was fedthrough a tube placed below the frit, and passed through the accumulatedaqueous nutrient in the form of small bubbles. The air then flowedthrough the packed bed of substrates containing the biomass. The testspecimen air flow rate was about 50 ml/min and it contained 12.3 mg ofBTEX per liter of air, which is essentially an overload concentrationfor an unacclimated reactor.

Equal volume of the 2 liter culture was added to each column and theexcess was drained out in order to inoculate the substrates in thecolumns. The inoculated reactor was then ran for about 300 hours and theeffluent air-streams were analyzed for their BTEX contents. The resultsare shown in FIG. 2-6.

FIG. 2, which is a graphic presentation of the benzene content of theeffluent air of the experiment, demonstrates that columns 1 and 4, whichcontained the PAC coated substrates, initially absorbed benzene rapidlyuntil the PAC was saturated. Once the PAC was saturated, the performanceof the columns deteriorated before they regained their remediationefficiency. It is believed that this phenomenon was due to the lowinitial biomass density in the bioreactor and the removal of benzenefrom the influent air by the PAC, depriving the carbon sources andresulting in the slowed growth of the microorganisms that metabolizebenzene. Once the PAC was saturated and benzene became available, themicroorganisms started to accumulate and thus started to remediatebenzene at a greater rate. The uncoated substrates in columns 2 and 3did not reduce the benzene content until about 270 hours into theexperiment, indicating that until that point, the bioreactor did nothave a sufficient biomass density to significantly reduce the benzenecontent of the influent air.

FIG. 3, which is a graphic presentation of the toluene content of theeffluent air of the columns, and FIG. 4, which presents ethylbenzenecontent, demonstrate similar results as discussed above for benzene.FIG. 5, which presents m- and p-xylene content, and FIG. 6, whichpresents o-xylene content, demonstrate that the microorganism densitiesfor the two test-specimen pollutant-remediating microorganisms did notincrease high enough to significantly reduce the pollutants in 300hours.

Example 4

Example 3 is continued for a longer time period to observe theperformance of the reactors when the bioreactors reach steady state.

Under the steady state condition, i.e., when the bioreactors accumulatean effectively high biomass density, the performance of column 2 issuperior to that of column 1, the performance of column 1 is better thanthat of column 4, and the performance of column 4 is better than that ofcolumn 3. It can be seen that the open space bodies and the PAC coatingimprove the performance of the bioreactors. In addition, when transientspike loads of pollutants are introduced into the influent air, thereactors with carbon coated substrates perform more evenly andsuperiorly than the reactors with uncoated substrates.

What is claimed is:
 1. A process for remediating vaporous pollutantswhich comprises passing a vaporous stream containing one or more ofpollutants through a bioreactor, said bioreactor comprising a pluralityof biologically active bodies, said biologically active body comprisinga macroporous substrate and one or more of microorganisms capable ofremediating one or more of said pollutants, wherein said substrate isfabricated from a decomposition-resistant material and wherein saidsubstrate is coated with a composition comprising an absorbent, abinder, a suspension aid, and a viscosity enhancer.
 2. The process forremediating vaporous pollutants of claim 1 wherein said bioreactorfurther comprises a feeding means that supplies a solution of nutrientsand buffers.
 3. The process for remediating vaporous pollutants of claim1 wherein said macroporous substrate comprises pores having an averagepore size of equal to or larger than about 0.1 cm.
 4. The process forremediating vaporous pollutants of claim 1 wherein said macroporoussubstrate comprises from about 40 volume % to about 98 volume % ofthroughpores.
 5. The process for remediating vaporous pollutants ofclaim 1 wherein said porous substrate is fabricated from a thermoplasticor a polyurethane.
 6. The process for remediating vaporous pollutants ofclaim 5 wherein said macroporous substrate is a polyurethane foam. 7.The process for remediating vaporous pollutants of claim 1 wherein saidmacroporous substrate is coated with an absorbent selected from thegroup consisting of coal, charcoal, carbon black, activated carbon,activated charcoal, silica gel, active clays, zeolites, ion exchangeresins and molecular sieves.
 8. The process for remediating vaporouspollutants of claim 1 wherein said bioreactor further comprises aplurality of open space bodies.
 9. The process for remediating vaporouspollutants of claim 8 wherein said open space bodies are coated with anabsorbent.